Light redirecting films and film systems

ABSTRACT

Light redirecting film comprises a thin optically transparent substrate having a pattern of individual optical elements formed as projections on a light exit surface of the film. At least some of the projections comprise a dome-shaped surface on the light exit surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/726,017, filed Mar. 17, 2010, which is a division of U.S. patentapplication Ser. No. 12/033,046, filed Feb. 19, 2008, now U.S. Pat. No.7,712,932, dated May 11, 2010, which is a division of U.S. patentapplication Ser. No. 10/954,551, filed Sep. 30, 2004, now U.S. Pat. No.7,364,341, dated Apr. 29, 2008, which is a continuation-in-part of U.S.patent application Ser. No. 10/729,113, filed Dec. 5, 2003, now U.S.Pat. No. 7,090,389, dated Aug. 15, 2006, which is a division of U.S.patent application Ser. No. 09/909,318, filed Jul. 19, 2001, now U.S.Pat. No. 6,752,505, dated Jun. 22, 2004, which is a continuation-in-partof U.S. patent application Ser. No. 09/256,275, filed Feb. 23, 1999, nowU.S. Pat. No. 6,712,481, dated Mar. 30, 2004, the entire disclosures ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to light redirecting films and film systems forredirecting light from a light source toward a direction normal to theplane of the films.

BACKGROUND OF THE INVENTION

Light redirecting films are thin transparent or translucent opticalfilms or substrates that redistribute the light passing through thefilms such that the distribution of the light exiting the films isdirected more normal to the surface of the films. Heretofore, lightredirecting films were provided with prismatic grooves, lenticulargrooves, or pyramids on the light exit surface of the films whichchanged the angle of the film/air interface for light rays exiting thefilms and caused the components of the incident light distributiontraveling in a plane perpendicular to the refracting surfaces of thegrooves to be redistributed in a direction more normal to the surface ofthe films. Such light redirecting films are used, for example, withliquid crystal displays, used in laptop computers, word processors,avionic displays, cell phones, PDAs and the like to make the displaysbrighter.

The light entrance surface of the films usually has a transparent ormatte finish depending on the visual appearance desired. A matte finishproduces a softer image but is not as bright due to the additionalscattering and resultant light loss caused by the matte or diffusesurface.

Heretofore, most applications used two grooved film layers rotatedrelative to each other such that the grooves in the respective filmlayers are at 90 degrees relative to each other. The reason for this isthat a grooved light redirecting film will only redistribute, towardsthe direction normal to the film surface, the components of the incidentlight distribution traveling in a plane perpendicular to the refractingsurfaces of the grooves. Therefore, to redirect light toward the normalof the film surface in two dimensions, two grooved film layers rotated90 degrees with respect to each other are needed, one film layer toredirect light traveling in a plane perpendicular to the direction ofits grooves and the other film layer to redirect light traveling in aplane perpendicular to the direction of its grooves.

Attempts have been made in the past to create a single layer lightredirecting film that will redirect components of the incident lightdistribution traveling along two different axes 90 degrees to eachother. One known way of accomplishing this is to provide a single layerfilm with two sets of grooves extending perpendicular to each otherresulting in a pyramid structure which redirects light traveling in bothsuch directions. However, such a film produces a much lower brightnessthan two film layers each with a single groove configuration rotated 90degrees with respect to each other because the area that is removed fromthe first set of grooves by the second set of grooves in a single layerfilm reduces the surface area available to redirect light substantiallyby 50% in each direction of travel.

In addition, heretofore, the grooves of light redirecting films havebeen constructed so that all of the grooves meet the surface of thefilms at the same angle, mostly 45 degrees. This design assumes aconstant, diffuse angular distribution of light from the light source,such as a lambertian source, a backlighting panel using a printing oretching technology to extract light, or a backlighting panel behindheavy diffusers. A light redirecting film where all of the lightredirecting surfaces meet the film at the same angle is not optimizedfor a light source that has a nonuniform directional component to itslight emission at different areas above the source. For example, theaverage angle about which a modern high efficiency edge lit backlight,using grooves or micro-optical surfaces to extract light, changes atdifferent distances from the light source, requiring a different anglebetween the light redirecting surfaces and the plane of the film tooptimally redirect light toward the normal of the film.

There is thus a need for a light redirecting film that can produce asofter image while eliminating the decrease in brightness associatedwith a matte or diffuse finish on the light input side of the film.Also, there is a need for a single layer of film which can redirect aportion of the light traveling in a plane parallel to the refractingsurfaces in a grooved film, that would be brighter than a single layerof film using prismatic or lenticular grooves. In addition, there is aneed for a light redirecting film that can compensate for the differentangular distributions of light that may exist for a particular lightsource at different positions above the source, such as backlights usedto illuminate liquid crystal displays. Also, there is a need for a lightredirecting film system in which the film is matched or tuned to thelight output distribution of a backlight or other light source toreorient or redirect more of the incident light from the backlightwithin a desired viewing angle.

SUMMARY OF THE INVENTION

The present invention relates to light redirecting films and lightredirecting film systems that redistribute more of the light emitted bya backlight or other light source toward a direction more normal to theplane of the films, and to light redirecting films that produce a softerimage without the brightness decrease associated with films that have amatte or diffuse finish on the light entrance surface of the films, forincreased effectiveness.

The light exit surface of the films has a pattern of discrete individualoptical elements of well defined shape for refracting the incident lightdistribution such that the distribution of light exiting the films is ina direction more normal to the surface of the films. These individualoptical elements may be formed by depressions in or projections on theexit surface of the films, and include one or more sloping surfaces forrefracting the incident light toward a direction normal to the exitsurface. These sloping surfaces may for example include a combination ofplanar and curved surfaces that redirect the light within a desiredviewing angle. Also, the curvature of the surfaces, or the ratio of thecurved area to the planar area of the individual optical elements aswell as the perimeter shapes of the curved and planar surfaces may bevaried to tailor the light output distribution of the films, tocustomize the viewing angle of the display device used in conjunctionwith the films. In addition, the curvature of the surfaces, or the ratioof the curved area to the planar area of the individual optical elementsmay be varied to redirect more or less light that is traveling in aplane that would be parallel to the grooves of a prismatic or lenticulargrooved film. Also the size and population of the individual opticalelements, as well as the curvature of the surfaces of the individualoptical elements may be chosen to produce a more or less diffuse outputor to randomize the input light distribution from the light source toproduce a softer more diffuse light output distribution whilemaintaining the output distribution within a specified angular regionabout the direction normal to the films.

The light entrance surface of the films may have an optical coating suchas an antireflective coating, a reflective polarizer, a retardationcoating, a polarization recycling coating or a polarizer. Also a matteor diffuse texture may be provided on the light entrance surfacedepending on the visual appearance desired. A matte finish produces asofter image but is not as bright.

The films may be constructed of single or multiple materials or layersof materials, and may have regions or layers with different indices ofrefraction. In addition, particles can be added to the films in order toproduce a desired optical effect.

The individual optical elements on the exit surface of the films may berandomized in such a way as to eliminate any interference with the pixelspacing of a liquid crystal display. This randomization can include thesize, shape, position, depth, orientation, angle or density of theoptical elements. This eliminates the need for diffuser layers to defeatmoiré and similar effects. This randomization and/or providing curvedsurfaces on the individual optical elements can also be used to break upthe image of the backlight. Further, at least some of the individualoptical elements may be arranged in groupings across the exit surface ofthe films, with at least some of the optical elements in each of thegroupings having a different size or shape characteristic thatcollectively produce an average size or shape characteristic for each ofthe groupings that varies across the films to obtain averagecharacteristic values beyond machining tolerances for any single opticalelement and to defeat moiré and interference effects with the pixelspacing of a liquid crystal display. In addition, at least some of theindividual optical elements may be oriented at different angles relativeto each other for customizing the ability of the films toreorient/redirect light along two different axes.

The angles that the light redirecting surfaces of the individual opticalelements make with the light exit surface of the films may also bevaried across the display area of a liquid crystal display to tailor thelight redirecting function of the films to a light input distributionthat is non-uniform across the surface of the light source.

The individual optical elements of the light redirecting films alsodesirably overlap each other, in a staggered, interlocked and/orintersecting configuration, creating an optical structure with excellentsurface area coverage. Moreover, the individual optical elements may bearranged in groupings with some of the individual optical elementsoriented along one axis and other individual optical elements orientedalong another axis. Also, the orientation of the individual opticalelements in each grouping may vary. Further, the size, shape, positionand/or orientation of the individual optical elements of the lightredirecting films may vary to account for variations in the distributionof light emitted by a light source.

The properties and pattern of the optical elements of light redirectingfilms may also be customized to optimize the light redirecting films fordifferent types of light sources which emit different lightdistributions, for example, one pattern for single bulb laptops, anotherpattern for double bulb flat panel displays, and so on.

Further, light redirecting film systems are provided in which theorientation, size, position and/or shape of the individual opticalelements of the light redirecting films are tailored to the light outputdistribution of a backlight or other light source to reorient orredirect more of the incident light from the backlight within a desiredviewing angle. Also, the backlight may include individual opticaldeformities that collimate light along one axis and the lightredirecting films may include individual optical elements that collimatelight along another axis perpendicular to the one axis.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter more fully described andparticularly pointed out in the claims, the following description andannexed drawings setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of butseveral of the various ways in which the principles of the invention maybe employed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the annexed drawings:

FIG. 1 is a schematic side elevation view of one form of lightredirecting film system in accordance with the present invention;

FIG. 2 is an enlarged fragmentary side elevation view of a portion ofthe backlight and light redirecting film system of FIG. 1;

FIGS. 3 and 4 are schematic side elevation views of other forms of lightredirecting film systems of the present invention;

FIGS. 5-20 are schematic perspective or plan views showing differentpatterns of individual optical elements on light redirecting films ofthe present invention;

FIGS. 5 a-5 n are schematic perspective views of different geometricshapes that the individual optical elements on the light redirectingfilms may take;

FIG. 21 is a schematic perspective view of a light redirecting filmhaving optical grooves extending across the film in a curved patternfacing a corner of the film;

FIG. 22 is a top plan view of a light redirecting film having a patternof optical grooves extending across the film facing a midpoint on oneedge of the film that decreases in curvature as the distance from theone edge increases;

FIG. 23 is an end elevation view of the light redirecting film of FIG.22 as seen from the left end thereof;

FIG. 24 is a side elevation view of the light redirecting film of FIG.22;

FIGS. 25 and 26 are enlarged schematic fragmentary plan views of asurface area of a backlight/light emitting panel assembly showingvarious forms of optical deformities formed on or in a surface of thebacklight;

FIGS. 27 and 28 are enlarged longitudinal sections through one of theoptical deformities of FIGS. 25 and 26, respectively;

FIGS. 29 and 30 are enlarged schematic longitudinal sections throughother forms of optical deformities formed on or in a surface of abacklight;

FIGS. 31-39 are enlarged schematic perspective views of backlightsurface areas containing various patterns of individual opticaldeformities of other well defined shapes;

FIG. 40 is an enlarged schematic longitudinal section through anotherform of optical deformity formed on or in a surface of a backlight;

FIGS. 41 and 42 are enlarged schematic top plan views of backlightsurface areas containing optical deformities similar in shape to thoseshown in FIGS. 37 and 38 arranged in a plurality of straight rows alongthe length and width of the surface areas;

FIGS. 43 and 44 are enlarged schematic top plan views of backlightsurface areas containing optical deformities also similar in shape tothose shown in FIGS. 37 and 38 arranged in staggered rows along thelength of the surface areas;

FIGS. 45 and 46 are enlarged schematic top plan views of backlightsurface areas containing a random or variable pattern of different sizedoptical deformities on the surface areas;

FIG. 47 is an enlarged schematic perspective view of a backlight surfacearea showing optical deformities increasing in size as the distance ofthe deformities from the light input surface increases or intensity ofthe light increases along the length of the surface area;

FIGS. 48 and 49 are schematic perspective views showing differentangular orientations of the optical deformities along the length andwidth of a backlight surface area;

FIGS. 50 and 51 are enlarged perspective views schematically showing howexemplary light rays emitted from a focused light source are reflectedor refracted by different individual optical deformities of well definedshapes of a backlight surface area;

FIGS. 52 and 54 are enlarged schematic plan views of two individualoptical elements of well defined shape on or in a surface of anoptically transparent substrate of a light redirecting film, each of theoptical elements having a flat surface and a curved surface that cometogether to form a ridge, and the optical elements intersecting eachother along different portions of the curved surfaces of the opticalelements;

FIGS. 53 and 55 are schematic perspective views of the optical elementsof FIGS. 52 and 54, respectively;

FIG. 56 is an enlarged perspective view schematically showing anindividual optical element on or in a surface of an opticallytransparent substrate of a light redirecting film having an asymmetricshape with two curved sides or surfaces;

FIG. 57 is a schematic plan view showing two of the optical elements ofFIG. 56 intersecting each other;

FIG. 58 is a schematic perspective view of the optical elements of FIG.57;

FIG. 59 is an enlarged schematic fragmentary plan view of a portion of apattern of individual non-interlockable optical elements of well definedshape on or in a surface of an optically transparent substrate of alight redirecting film, the non-interlockable optical elements beingarranged to maximize coverage of the surface of the substrate occupiedthereby without intersecting each other;

FIGS. 60 and 61 are enlarged schematic fragmentary plan views ofportions of patterns of individual non-interlockable optical elements ofwell defined shape on or in a surface of an optically transparentsubstrate of a light redirecting film similar to FIG. 59, but showingthe non-interlockable optical elements intersecting each other indifferent amounts to increase the amount of coverage of the surface ofthe substrate occupied by the non-interlockable optical elements;

FIGS. 62-64 are enlarged schematic plan views of non-interlockableoptical elements attached or fitted to different interlockable geometricshapes;

FIG. 65 is an enlarged plan view of one form of nonrandomized pattern ofnon-interlockable wedge shaped optical elements;

FIG. 66 is an enlarged plan view of one form of randomized pattern ofnon-interlockable wedge shaped optical elements;

FIG. 67 is an enlarged schematic perspective view showing a radialpattern of optical elements on or in a surface of a light redirectingfilm;

FIG. 68 is an enlarged schematic perspective view of an individualoptical element of a light redirecting film having only two surfaces, aflat or planar surface and a curved surface that come together to form adistinct ridge;

FIG. 69 is an enlarged schematic perspective view of another individualoptical element of a light redirecting film having multiple pairs ofsurfaces that come together to form a plurality of distinct ridges;

FIG. 70 is an enlarged schematic perspective view of an individualoptical element shape similar to that shown in FIG. 68 except that theoptical element of FIG. 70 has a non-distinct, rounded ridge where thetwo surfaces come together;

FIG. 71 is an enlarged schematic perspective view of an individualoptical element shape also similar to that shown in FIG. 69 except thatthe optical element of FIG. 71 has a non-distinct ridge with aflattened, rounded, curved or otherwise misshaped peak that reduces thepeak depth or height of the optical element;

FIGS. 72 and 73 are further enlarged schematic perspective views of theindividual optical element shapes of FIGS. 70 and 71, respectively,showing various dimensional characteristics of such optical elements;

FIGS. 74-78 are schematic side elevation views of still other forms oflight redirecting film systems of the present invention; and

FIGS. 79 and 80 are schematic perspective views of still other forms oflight redirecting film systems of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 schematically show one form of light redirecting filmsystem 1 in accordance with this invention including a light redirectingfilm 2 that redistributes more of the light emitted by a backlight BL orother light source toward a direction more normal to the surface of thefilm. Film 2 may be used to redistribute light within a desired viewingangle from almost any light source for lighting, for example, a displayD such as a liquid crystal display, used in laptop computers, wordprocessors, avionic displays, cell phones, PDAs and the like, to makethe displays brighter. The liquid crystal display can be any typeincluding a transmissive liquid crystal display as schematically shownin FIGS. 1 and 2, a reflective liquid crystal display as schematicallyshown in FIG. 3 and a transflective liquid crystal display asschematically shown in FIG. 4.

The reflective liquid crystal display D shown in FIG. 3 includes a backreflector 40 adjacent the back side for reflecting ambient lightentering the display back out the display to increase the brightness ofthe display. The light redirecting film 2 of the present invention isplaced adjacent the top of the reflective liquid crystal display toredirect ambient light (or light from a front light) into the displaytoward a direction more normal to the plane of the film for reflectionback out by the back reflector within a desired viewing angle toincrease the brightness of the display. Light redirecting film 2 may beattached to, laminated to or otherwise held in place against the top ofthe liquid crystal display.

The transflective liquid crystal display D shown in FIG. 4 includes atransreflector T placed between the display and a backlight BL forreflecting ambient light entering the front of the display back out thedisplay to increase the brightness of the display in a lightedenvironment, and for transmitting light from the backlight through thetransreflector and out the display to illuminate the display in a darkenvironment. In this embodiment the light redirecting film 2 may eitherbe placed adjacent the top of the display or adjacent the bottom of thedisplay or both as schematically shown in FIG. 4 for redirecting orredistributing ambient light and/or light from the backlight more normalto the plane of the film to make the light ray output distribution moreacceptable to travel through the display to increase the brightness ofthe display.

Light redirecting film 2 comprises a thin transparent film or substrate8 having a pattern of discrete individual optical elements 5 of welldefined shape on the light exit surface 6 of the film for refracting theincident light distribution such that the distribution of the lightexiting the film is in a direction more normal to the surface of thefilm.

Each of the individual optical elements 5 has a width and length manytimes smaller than the width and length of the film, and may be formedby depressions in or projections on the exit surface of the film. Theseindividual optical elements 5 include at least one sloping surface forrefracting the incident light toward the direction normal to the lightexit surface. FIG. 5 shows one pattern of individual optical elements 5on a film 2. These optical elements may take many different shapes. Forexample, FIG. 5 a shows a non-prismatic optical element 5 having a totalof two surfaces 10, 12, both of which are sloping. One of the surfaces10 shown in FIG. 5 a is planar or flat whereas the other surface 12 iscurved. Moreover, both surfaces 10, 12 intersect each other and alsointersect the surface of the film. Alternatively, both surfaces 10, 12of the individual optical elements may be curved as schematically shownin FIG. 5 b.

Alternatively, the optical elements 5 may each have only one surfacethat is curved and sloping and intersects the film. FIG. 5 c shows onesuch optical element 5 in the shape of a cone 13, whereas FIG. 5 d showsanother such optical element having a semispherical or dome shape 14.Also, such optical elements may have more than one sloping surfaceintersecting the film.

FIG. 5 e shows an optical element 5 having a total of three surfaces,all of which intersect the film and intersect each other. Two of thesurfaces 15 and 16 are curved, whereas the third surface 17 is planar.

FIG. 5 f shows an optical element 5 in the shape of a pyramid 18 withfour triangular shaped sides 19 that intersect each other and intersectthe film. The sides 19 of the pyramid 18 may all be of the same size andshape as shown in FIG. 5 f, or the sides 19 of the pyramids 18 may bestretched so the sides have different perimeter shapes as shown in FIG.5 g. Also, the optical elements 5 may have any number of planar slopingsides. FIG. 5 h shows an optical element 5 with four planar slopingsides 20, whereas FIG. 5 i shows an optical element 5 with eight planarsloping sides 20.

The individual optical elements 5 may also have more than one curved andmore than one planar sloping surface, all intersecting the film. FIG. 5j shows an optical element 5 having a pair of intersecting oppositelysloping planar sides 22 and oppositely rounded or curved ends or sides23. Further, the sloping planar sides 22 and curved ends or sides 23 mayhave different angled slopes as shown in FIGS. 5 k and 5 l. Moreover,the optical elements 5 may have at least one curved surface that doesnot intersect the film. One such optical element 5 is shown in FIG. 5 mwhich includes a pair of oppositely sloping planar sides 22 andoppositely rounded or curved ends or sides 23 and a rounded or curvedtop 24 intersecting the oppositely sloping sides and oppositely roundedends. Further, the optical elements 5 may be curved along their lengthas shown in FIG. 5 n. In addition, at least some of the surfaces of theoptical elements 5 may be optically smooth, or have a texture, coating,or other surface treatment applied, in order to produce a specificoptical effect and/or to tailor the optical properties of the lightredirecting film to suit a particular application.

Providing the individual optical elements 5 with a combination of planarand curved surfaces redirects or redistributes a larger viewing areathan is possible with a grooved film. Also, the curvature of thesurfaces, or the ratio of the curved area to the planar area of theindividual optical elements may be varied to tailor the light outputdistribution of the film to customize the viewing area of a displaydevice used in conjunction with the film.

The light entrance surface 7 of the film 2 may have an optical coating25 (see FIG. 2) such as an antireflective coating, a reflectivepolarizer, a retardation coating, a polarization recycling coating or apolarizer. Also, a matte or diffuse texture may be provided on the lightentrance surface 7 depending on the visual appearance desired. A mattefinish produces a softer image but is not as bright. The combination ofplanar and curved surfaces of the individual optical elements 5 of thepresent invention may be configured to redirect some of the light raysimpinging thereon in different directions to produce a softer imagewithout the need for an additional diffuser or matte finish on theentrance surface of the film.

The individual optical elements 5 of the light redirecting film 2 alsodesirably overlap each other in a staggered, interlocked and/orintersecting configuration, creating an optical structure with excellentsurface area coverage. FIGS. 6, 7, 13 and 15, for example, show opticalelements 5 staggered with respect to each other; FIGS. 8-10 show theoptical elements 5 intersecting each other; and FIGS. 11 and 12 show theoptical elements 5 interlocking each other.

Moreover, the slope angle, density, position, orientation, height ordepth, shape, and/or size of the optical elements 5 of the lightredirecting film 2 may be matched or tuned to the particular lightoutput distribution of a backlight BL or other light source to accountfor variations in the distribution of light emitted by the backlight inorder to redistribute more of the light emitted by the backlight withina desired viewing angle. For example, the angle that the slopingsurfaces (e.g., surfaces 10, 12) of the optical elements 5 make with thesurface of the light redirecting film 2 may be varied as the distancefrom the backlight BL from a light source 26 increases to account forthe way the backlight emits light rays R at different angles as thedistance from the light source increases as schematically shown in FIG.2. Also, the backlight BL itself may be designed to emit more of thelight rays at lower angles to increase the amount of light emitted bythe backlight and rely on the light redirecting film 2 to redistributemore of the emitted light within a desired viewing angle. In this waythe individual optical elements 5 of the light redirecting film 2 may beselected to work in conjunction with the optical deformations of thebacklight to produce an optimized output light ray angle distributionfrom the system.

FIGS. 2, 5 and 9 show different patterns of individual optical elements5 all of the same height or depth, whereas FIGS. 7, 8, 10, 13 and 14show different patterns of individual optical elements 5 of differentshapes, sizes and height or depth.

The individual optical elements 5 may also be randomized on the film 2as schematically shown in FIGS. 16 and 17 in such a way as to eliminateany interference with the pixel spacing of a liquid crystal display.This eliminates the need for optical diffuser layers 30 shown in FIGS. 1and 2 to defeat moiré and similar effects. Moreover, at least some ofthe individual optical elements 5 may be arranged in groupings 32 acrossthe film, with at least some of the optical elements 5 in each groupinghaving a different size or shape characteristic that collectivelyproduce an average size or shape characteristic for each of thegroupings that varies across the film as schematically shown in FIGS. 7,13 and 15 to obtain characteristic values beyond machining tolerances todefeat moiré and interference effects with the liquid crystal displaypixel spacing. For example, at least some of the optical elements 5 ineach grouping 32 may have a different depth or height that collectivelyproduce an average depth or height characteristic for each grouping thatvaries across the film. Also, at least some of the optical elements ineach grouping may have a different slope angle that collectively producean average slope angle for each grouping that varies across the film.Further, at least one sloping surface of the individual optical elementsin each grouping may have a different width or length that collectivelyproduce an average width or length characteristic in each grouping thatvaries across the film.

Where the individual optical elements 5 include a combination of planarand curved surfaces 10, 12, the curvature of the curved surfaces 12, orthe ratio of the curved area to the planar area of the individualoptical elements as well as the perimeter shapes of the curved andplanar surfaces may be varied to tailor the light output distribution ofthe film. In addition, the curvature of the curved surfaces, or theratio of the curved area to the planar area of the individual opticalelements may be varied to redirect more or less light that is travelingin a plane that would be parallel to the grooves of a prismatic orlenticular grooved film, partially or completely replacing the need fora second layer of light redirecting film. Also, at least some of theindividual optical elements may be oriented at different angles relativeto each other as schematically shown in FIGS. 13 and 16 to redistributemore of the light emitted by a light source along two different axes ina direction more normal to the surface of the film, partially orcompletely replacing the need for a second layer of light redirectingfilm. However, it will be appreciated that two layers of such lightredirecting film each having the same or different patterns ofindividual optical elements 5 thereon may be placed between a lightsource and viewing area with the layers rotated 90 degrees (or otherangles greater than 0 degrees and less than 90 degrees) with respect toeach other so that the individual optical elements on the respectivefilm layers redistribute more of the light emitted by a light sourcetraveling in different planar directions in a direction more normal tothe surface of the respective films.

Also, the light redirecting film 2 may have a pattern of opticalelements 5 that varies at different locations on the film asschematically shown in FIG. 15 to redistribute the light ray outputdistribution from different locations of a backlight or other lightsource to redistribute the light ray output distribution from thedifferent locations toward a direction normal to the film.

Further, the properties and pattern of the optical elements of the lightredirecting film may be customized to optimize the light redirectingfilm for different types of light sources which emit different lightdistributions, for example, one pattern for single bulb laptops, anotherpattern for double bulb flat panel displays, and so on.

FIG. 17 shows the optical elements 5 arranged in a radial pattern fromthe outside edges of the film 2 toward the center to redistribute thelight ray output distribution of a backlight BL that receives light fromcold cathode fluorescent lamps 26 along all four side edges of thebacklight.

FIG. 18 shows the optical elements 5 arranged in a pattern of angledgroupings 32 across the film 2 that are tailored to redistribute thelight ray output distribution of a backlight BL that receives light fromone cold cathode fluorescent lamp 26 or a plurality of light emittingdiodes 26 along one input edge of the backlight.

FIG. 19 shows the optical elements 5 arranged in a radial type patternfacing a corner of the film 2 to redistribute the light ray outputdistribution of a backlight BL that is corner lit by a light emittingdiode 26. FIG. 20 shows the optical elements 5 arranged in a radial typepattern facing a midpoint on one input edge of the film 2 toredistribute the light ray output distribution of a backlight BL that islighted at a midpoint of one input edge of the backlight by a singlelight emitting diode 26.

FIG. 21 shows a light redirecting film 2 having optical grooves 35extending across the film in a curved pattern facing a corner of thefilm to redistribute the light ray output distribution of a backlight BLthat is corner lit by a light emitting diode 26, whereas FIGS. 22-24show a light redirecting film 2 having a pattern of optical grooves 35extending across the film facing a midpoint along one edge of the filmthat decreases in curvature as the distance from the one edge increasesto redistribute the light ray output distribution of a backlight BL thatis edge lit by a light emitting diode 26 at a midpoint of one input edgeof the backlight.

Where the light redirecting film 2 has a pattern 40 of optical elements5 thereon that varies along the length of the film, a roll 41 of thefilm 2 may be provided having a repeating pattern of optical elementsthereon as schematically shown in FIG. 15 to permit a selected area ofthe pattern that best suits a particular application to be die cut fromthe roll of film.

The backlight BL may be substantially flat, or curved, or may be asingle layer or multi-layers, and may have different thicknesses andshapes as desired. Moreover, the backlight may be flexible or rigid, andbe made of a variety of compounds. Further, the backlight may be hollow,filled with liquid, air, or be solid, and may have holes or ridges.

Also, the light source 26 may be of any suitable type including, forexample, an arc lamp, an incandescent bulb which may also be colored,filtered or painted, a lens end bulb, a line light, a halogen lamp, alight emitting diode (LED), a chip from an LED, a neon bulb, a coldcathode fluorescent lamp, a fiber optic light pipe transmitting from aremote source, a laser or laser diode, or any other suitable lightsource. Additionally, the light source 26 may be a multiple colored LED,or a combination of multiple colored radiation sources in order toprovide a desired colored or white light output distribution. Forexample, a plurality of colored lights such as LEDs of different colors(e.g., red, blue, green) or a single LED with multiple color chips maybe employed to create white light or any other colored light outputdistribution by varying the intensities of each individual coloredlight.

A pattern of optical deformities may be provided on one or both sides ofthe backlight BL or on one or more selected areas on one or both sidesof the backlight as desired. As used herein, the term opticaldeformities means any change in the shape or geometry of a surfaceand/or coating or surface treatment that causes a portion of the lightto be emitted from the backlight. These deformities can be produced in avariety of manners, for example, by providing a painted pattern, anetched pattern, machined pattern, a printed pattern, a hot stamppattern, or a molded pattern or the like on selected areas of thebacklight. An ink or print pattern may be applied for example by padprinting, silk printing, inkjet, heat transfer film process or the like.The deformities may also be printed on a sheet or film which is used toapply the deformities to the backlight. This sheet or film may become apermanent part of the backlight for example by attaching or otherwisepositioning the sheet or film against one or both sides of the backlightin order to produce a desired effect.

By varying the density, opaqueness or translucence, shape, depth, color,area, index of refraction or type of deformities on or in an area orareas of the backlight, the light output of the backlight can becontrolled. The deformities may be used to control the percent of lightoutput from a light emitting area of the backlight. For example, lessand/or smaller size deformities may be placed on surface areas whereless light output is wanted. Conversely, a greater percentage of and/orlarger deformities may be placed on surface areas of the backlight wheregreater light output is desired.

Varying the percentages and/or size of deformities in different areas ofthe backlight is necessary in order to provide a substantially uniformlight output distribution. For example, the amount of light travelingthrough the backlight will ordinarily be greater in areas closer to thelight source than in other areas further removed from the light source.A pattern of deformities may be used to adjust for the light varianceswithin the backlight, for example, by providing a denser concentrationof deformities with increased distance from the light source therebyresulting in a more uniform light output distribution from thebacklight.

The deformities may also be used to control the output ray angledistribution from the backlight to suit a particular application. Forexample, if the backlight is used to backlight a liquid crystal display,the light output will be more efficient if the deformities (or a lightredirecting film 2 is used in combination with the backlight) direct thelight rays emitted by the backlight at predetermined ray angles suchthat they will pass through the liquid crystal display with low loss.Additionally, the pattern of optical deformities may be used to adjustfor light output variances attributed to light extractions of thebacklight. The pattern of optical deformities may be printed on thebacklight surface areas utilizing a wide spectrum of paints, inks,coatings, epoxies or the like, ranging from glossy to opaque or both,and may employ half-tone separation techniques to vary the deformitycoverage. Moreover, the pattern of optical deformities may be multiplelayers or vary in index of refraction.

Print patterns of optical deformities may vary in shapes such as dots,squares, diamonds, ellipses, stars, random shapes, and the like. Also,print patterns of sixty lines per inch or finer are desirably employed.This makes the deformities or shapes in the print patterns nearlyinvisible to the human eye in a particular application, therebyeliminating the detection of gradient or banding lines that are commonto light extracting patterns utilizing larger elements. Additionally,the deformities may vary in shape and/or size along the length and/orwidth of the backlight. Also, a random placement pattern of thedeformities may be utilized throughout the length and/or width of thebacklight. The deformities may have shapes or a pattern with no specificangles to reduce moiré or other interference effects. Examples ofmethods to create these random patterns are printing a pattern of shapesusing stochastic print pattern techniques, frequency modulated half tonepatterns, or random dot half tones. Moreover, the deformities may becolored in order to effect color correction in the backlight. The colorof the deformities may also vary throughout the backlight, for example,to provide different colors for the same or different light outputareas.

In addition to or in lieu of the patterns of optical deformities, otheroptical deformities including prismatic or lenticular grooves or crossgrooves, or depressions or raised surfaces of various shapes using morecomplex shapes in a mold pattern may be molded, etched, stamped,thermoformed, hot stamped or the like into or on one or more surfaceareas of the backlight. The prismatic or lenticular surfaces,depressions or raised surfaces will cause a portion of the light rayscontacted thereby to be emitted from the backlight. Also, the angles ofthe prisms, depressions or other surfaces may be varied to direct thelight in different directions to produce a desired light outputdistribution or effect. Moreover, the reflective or refractive surfacesmay have shapes or a pattern with no specific angles to reduce moiré orother interference effects.

A back reflector 40 may be attached or positioned against one side ofthe backlight BL as schematically shown in FIGS. 1 and 2 in order toimprove light output efficiency of the backlight by reflecting the lightemitted from that side back through the backlight for emission throughthe opposite side. Additionally, a pattern of optical deformities 50 maybe provided on one or both sides of the backlight as schematically shownin FIGS. 1 and 2 in order to change the path of the light so that theinternal critical angle is exceeded and a portion of the light isemitted from one or both sides of the backlight.

FIGS. 25-28 show optical deformities 50 which may either be individualprojections 51 on the respective backlight surface areas 52 orindividual depressions 53 in such surface areas. In either case, each ofthese optical deformities 50 has a well defined shape including areflective or refractive surface 54 that intersects the respectivebacklight surface area 52 at one edge 55 and has a uniform slopethroughout its length for more precisely controlling the emission oflight by each of the deformities. Along a peripheral edge portion 56 ofeach reflective/refractive surface 54 is an end wall 57 of eachdeformity 50 that intersects the respective panel surface area 52 at agreater included angle I than the included angle I′ between thereflective/refractive surfaces 54 and the panel surface area 52 (seeFIGS. 27 and 28) to minimize the projected surface area of the end wallson the panel surface area. This allows more deformities 50 to be placedon or in the panel surface areas than would otherwise be possible if theprojected surface areas of the end walls 57 were substantially the sameas or greater than the projected surface areas of thereflective/refractive surfaces 54.

In FIGS. 25 and 26 the peripheral edge portions 56 of thereflective/refractive surfaces 54 and associated end walls 57 are curvedin the transverse direction. Also in FIGS. 27 and 28 the end walls 57 ofthe deformities 50 are shown extending substantially perpendicular tothe reflective/refractive surfaces 54 of the deformities. Alternatively,such end walls 57 may extend substantially perpendicular to the panelsurface areas 52 as schematically shown in FIGS. 29 and 30. Thisvirtually eliminates any projected surface area of the end walls 57 onthe panel surface areas 52 whereby the density of the deformities on thepanel surface areas may be even further increased.

The optical deformities may also be of other well defined shapes toobtain a desired light output distribution from a panel surface area.FIG. 31 shows individual light extracting deformities 58 on a panelsurface area 52 each including a generally planar, rectangularreflective/refractive surface 59 and associated end wall 60 of a uniformslope throughout their length and width and generally planar sidewalls61. Alternatively, the deformities 58′ may have rounded or curvedsidewalls 62 as schematically shown in FIG. 32.

FIG. 33 shows individual light extracting deformities 63 on a panelsurface area 52 each including a planar, sloping triangular shapedreflective/refractive surface 64 and associated planar, generallytriangularly shaped sidewalls or end walls 65. FIG. 34 shows individuallight extracting deformities 66 each including a planar slopingreflective/refractive surface 67 having angled peripheral edge portions68 and associated angled end and sidewalls 69 and 70.

FIG. 35 shows individual light extracting deformities 71 which aregenerally conically shaped, whereas FIG. 36 shows individual lightextracting deformities 72 each including a rounded reflective/refractivesurface 73 and rounded end walls 74 and rounded or curved sidewalls 75all blended together. These additional surfaces will reflect or refractother light rays impinging thereon in different directions to spreadlight across the backlight/panel member BL to provide a more uniformdistribution of light emitted from the panel member.

Regardless of the particular shape of the reflective/refractive surfacesand end and sidewalls of the individual deformities, such deformitiesmay also include planar surfaces intersecting the reflective/refractivesurfaces and end and/or sidewalls in parallel spaced relation to thepanel surface areas 52. FIGS. 37-39 show deformities 76, 77 and 78 inthe form of individual projections on a panel surface area havingrepresentative shapes similar to those shown in FIGS. 31, 32 and 35,respectively, except that each deformity is intersected by a planarsurface 79 in parallel spaced relation to the panel surface area 52. Inlike manner, FIG. 40 shows one of a multitude of deformities 80 in theform of individual depressions 81 in a panel surface area 52 eachintersected by a planar surface 79 in parallel spaced relation to thegeneral planar surface of the panel surface area 52. Any light rays thatimpinge on such planar surfaces 79 at internal angles less than thecritical angle for emission of light from the panel surface area 52 willbe internally reflected by the planar surfaces 79, whereas any lightrays impinging on such planar surfaces 79 at internal angles greaterthan the critical angle will be emitted by the planar surfaces withminimal optical discontinuities, as schematically shown in FIG. 40.

Where the deformities are projections on the panel surface area 52, thereflective/refractive surfaces extend at an angle away from the panel ina direction generally opposite to that in which the light rays from thelight source 26 travel through the panel as schematically shown in FIGS.27 and 29. Where the deformities are depressions in the panel surfacearea, the reflective/refractive surfaces extend at an angle into thepanel in the same general direction in which the light rays from thelight source 26 travel through the panel member as schematically shownin FIGS. 28 and 30.

Regardless of whether the deformities are projections or depressions onor in the panel surface areas 52, the slopes of the lightreflective/refractive surfaces of the deformities may be varied to causethe light rays impinging thereon to be either refracted out of the lightemitting panel or reflected back through the panel and emitted out theopposite side of the panel which may be etched to diffuse the lightemitted therefrom or covered by a light redirecting film 2 to produce adesired effect. Also, the pattern of optical deformities on the panelsurface area may be uniform or variable as desired to obtain a desiredlight output distribution from the panel surface areas. FIGS. 41 and 42show deformities 76 and 77 similar in shape to those shown in FIGS. 37and 38 arranged in a plurality of generally straight uniformly spacedapart rows along the length and width of a panel surface area 52,whereas FIGS. 43 and 44 show such deformities 76 and 77 arranged instaggered rows that overlap each other along the length of a panelsurface area.

Also, the size, including the width, length and depth or height as wellas the angular orientation and position of the optical deformities mayvary along the length and/or width of any given panel surface area toobtain a desired light output distribution from the panel surface area.FIGS. 45 and 46 show a random or variable pattern of different sizedeformities 58 and 58′ similar in shape to those shown in FIGS. 31 and32, respectively, arranged in staggered rows on a panel surface area 52,whereas FIG. 47 shows deformities 77 similar in shape to those shown inFIG. 38 increasing in size as the distance of the deformities from thelight source increases or intensity of the light decreases along thelength and/or width of the panel surface area. The deformities 58 and58′ are shown in FIGS. 45 and 46 arranged in clusters 82 across thepanel surface, with at least some of the deformities in each clusterhaving a different size or shape characteristic that collectivelyproduce an average size or shape characteristic for each of the clustersthat varies across the panel surface. For example, at least some of thedeformities in each of the clusters may have a different depth or heightor different slope or orientation that collectively produce an averagedepth or height characteristic or average slope or orientation of thesloping surface that varies across the panel surface. Likewise at leastsome of the deformities in each of the clusters may have a differentwidth or length that collectively produce an average width or lengthcharacteristic that varies across the panel surface. This allows one toobtain a desired size or shape characteristic beyond machinerytolerances, and also defeats moiré and interference effects.

FIGS. 48 and 49 schematically show different angular orientations ofoptical deformities 85 of any desired shape along the length and widthof a panel surface area 52. In FIG. 48 the deformities are arranged instraight rows 86 along the length of the panel surface area but thedeformities in each of the rows are oriented to face the light source 26so that all of the deformities are substantially in line with the lightrays being emitted from the light source. In FIG. 49 the deformities 85are also oriented to face the light source 26 similar to FIG. 48. Inaddition, the rows 87 of deformities in FIG. 49 are in substantialradial alignment with the light source 26.

FIGS. 50 and 51 schematically show how exemplary light rays 90 emittedfrom a focused light source 26 insert molded or cast within a lighttransition area 91 of a light emitting panel assembly BL in accordancewith this invention are reflected during their travel through the lightemitting panel member 92 until they impinge upon individual lightextracting deformities 50, 77 of well defined shapes on or in a panelsurface area 52 causing more of the light rays to be reflected orrefracted out of one side 93 of the panel member than the other side 94.In FIG. 50 the exemplary light rays 90 are shown being reflected by thereflective/refractive surfaces 54 of the deformities 50 in the samegeneral direction out through the same side 93 of the panel member,whereas in FIG. 51 the light rays 90 are shown being scattered indifferent directions within the panel member 92 by the rounded sidewalls62 of the deformities 77 before the light rays are reflected/refractedout of the same side 93 of the panel member. Such a pattern ofindividual light extracting deformities of well defined shapes inaccordance with the present invention can cause 60 to 70% or more of thelight received through the input edge 95 of the panel member to beemitted from the same side of the panel member.

As discussed previously, the individual optical elements of the lightredirecting films may overlap each other in a staggered, interlockingand/or intersecting configuration in order to create an opticalstructure with increased surface coverage to increase the on axis gainof the light exiting the light redirecting films. FIGS. 52-55 show twosuch individual optical elements 5 on a surface 96 of an opticallytransparent substrate 8 each having only one flat or planar surface 10and only one curved surface 12 that come together to form a ridge 97.Also, the curved surfaces 12 of the optical elements intersect eachother to increase the relative percentage of flat surface area 10 tocurved surface area 12 of the optical elements to further increase theon axis gain of light passing through the substrate. Depending on theorientation and position of the optical elements, the relativepercentage of the remaining flat surface area 10 to the remaining curvedsurface area 12 of the intersecting optical elements may be greater than60% or even greater than 75%.

The optical elements 5 shown in FIGS. 52-55 are of the same general sizeand shape and are oriented with their flat surfaces 10 facing inopposite directions and only their curved surfaces 12 intersecting eachother. Also in FIGS. 52 and 53 the optical elements 5 are in directalignment with each other in the width direction, whereas in FIGS. 54and 55 the optical elements are offset with respect to each other in thewidth direction. This offset allows more of the curved surfaces 12 ofthe optical elements to intersect each other without intersecting theflat surfaces 10 to maximize the relative percentage of the remainingflat surface area 10 to the remaining curved surface area 12 of theintersecting optical elements to maximize the on axis gain of lightpassing through the substrate while achieving substantially completesurface coverage of at least one of the surfaces of the substrateoccupied by the optical elements, for example, greater than 90% surfacecoverage.

FIG. 56 shows an optical element 5 on or in a surface 96 of an opticallytransparent substrate 8 of a light redirecting film that only has twosides or surfaces 10 and 12 that come together to form a ridge 97similar to the optical elements shown in FIGS. 52-55. However, theoptical element shown in FIG. 56 has an asymmetric shape. Also bothsides 10 and 12 are shown curved with one of the sides 12 having asmaller radius than the other side 10. Two such optical elements 5 areshown in FIGS. 57 and 58 intersecting each other to a greater extent onthe smaller radius surfaces 12 than on the larger radius surfaces 10 todecrease the relative percentage of the smaller radius surfaces 12 tothe larger radius surfaces 10 to increase on axis gain of light passingthrough the substrate 8.

Optical elements 5 having interlockable geometric shapes may also beoriented and placed to interlock each other to achieve substantiallycomplete surface coverage of at least one of the surfaces of thesubstrate occupied by the optical elements without intersecting eachother as schematically shown, for example, in FIGS. 11 and 12. However,at least some of the optical elements 5 may have a geometric shape thatprevents at least some of the optical elements from interlocking eachother, as when the optical elements only have one flat surface 10 andonly one curved surface 12 as shown, for example, in FIGS. 5, 5 a and52-55. In that event the non-interlockable optical elements 5 may stillbe oriented and placed to maximize the coverage of the surface of thesubstrate occupied by the non-interlockable optical elements.

FIG. 59 shows one such arrangement of non-interlockable optical elements5 that are oriented and placed in pairs 98 with the flat surfaces 10 ofthe optical elements of each pair in substantial abutting alignment witheach other. Also the pairs 98 of optical elements 5 are arranged instaggered rows 99 with the curved surfaces 12 of the optical elements ofeach pair in each row in substantially tangential contact with eachother, and the curved surfaces 12 of the optical elements 5 in each rowin substantially tangential contact with the curved surfaces of theoptical elements in each adjacent row to achieve very high coverage ofthe surface of the substrate occupied by the optical elements.

Because the non-interlockable optical elements 5 do not intersect in thearrangement shown in FIG. 59, some non-patterned area 100 between theoptical elements is preserved. The percentage of non-patterned area 100can be specified by tailoring the arrangement of the optical elements 5.For example, the amount of non-patterned surface area can be reduced asby decreasing the spacing of the optical elements 5 in the widthdirection and/or length direction to cause the optical elements 5 tointersect. Alternatively the amount of non-patterned area 100 can beincreased by increasing the spacing of the optical elements in the widthdirection and/or the length direction. This non-patterned area 100 maybe optically smooth, or have a texture, coating, or other surfacetreatment applied, in order to produce a specific optical effect and/orto tailor the optical properties of the light redirecting film for aparticular application. One way in which this non-patterned area 100 canbe used is to provide combined functionality that would normally requiremultiple optical films. For example, if the non-patterned area of onefilm had a light diffusing texture when compared to another lightredirecting film with substantially complete surface coverage of theoptical elements 5, the light output distribution of the one film wouldbe softer and the viewing angle of the one film would be increased,while the on axis gain of the one film would decrease slightly. Thisconfiguration of the one film would provide properties of both a lightredirecting film and a diffuser film in a single film.

Further, at least some of the optical elements 5 may be comprised of atleast two different shaped non-interlockable optical elements orientedand placed to maximize coverage of the portion of the surface of thesubstrate occupied by the optical elements without intersecting eachother as shown, for example, in FIGS. 8 and 14. Alternatively, at leastsome of the non-interlockable optical elements 5 may also be positionedto intersect each other to a greater or lesser extent to furtherincrease the amount of surface coverage of the substrate occupied by thenon-interlockable optical elements as schematically shown in FIG. 60 sothe coverage of the portion of the surface occupied by thenon-interlockable optical elements is substantially complete (forexample, greater than 90% complete). Also, at least some of thenon-interlockable optical elements 5 may be positioned to intersect eachother to a greater extent on the curved surfaces 12 of the opticalelements than on the flat surfaces 10 as schematically shown in FIG. 61to further increase the relative percentage of flat surface area tocurved surface area of the intersecting non-interlockable opticalelements to further increase the on axis gain of light passing throughthe substrate.

One way to construct these patterns of non-interlockable opticalelements is to attach or fit to each non-interlockable optical elementan interlockable geometrical shape that can be patterned in a twodimensional lattice with substantially complete surface coverage, theinterlockable geometrical shape being the basis shape for the lattice.FIGS. 62-64 show three such geometries. By choosing an appropriate basisshape the optical elements can be made to either intersect or notintersect as desired. For example, if the non-interlockable opticalelement 5 is substantially fully contained within the basis shape 101 asshown in FIG. 62, a pattern of such optical elements will substantiallynot intersect. Conversely, if the physical boundary of thenon-interlockable optical element 5 extends beyond the basis shape 102or 103 as shown in FIGS. 63 and 64, a pattern of such optical elementswill intersect.

FIGS. 59-61 show examples of different patterns of non-interlockablewedge shaped optical elements 5 resulting from the basis shapes 101-103shown in FIGS. 62-64, respectively. The percent surface coverage of alight redirecting film by a given pattern of non-interlockable opticalelements can also be easily determined from the basis shape. Forexample, in the basis shape 101 shown in FIG. 62, the ratio of theprojected area of the non-interlockable optical element over the area ofthe basis shape 101 is approximately 91%. Therefore the percent coverageof the surface of a light redirecting film occupied by non-interlockableoptical elements patterned as shown in FIG. 59 is also approximately91%.

Further, in order to reduce moiré and other interference effects, arandom perturbation may be introduced into the placement or position ofthe non-interlockable optical elements within the two dimensionallattice. In order to prevent the creation of additional non-patternedarea caused by this randomization process, the lattice spacing in eachdirection in which randomization is to be introduced is compressed bygreater than or approximately equal to the amount of the desiredrandomization in a given direction. This is equivalent to choosing anappropriate smaller basis shape for the given non-interlockable opticalelement than would be used if no randomization was present.

For example, choosing the basis 102 shown in FIG. 63 for a randomizedversion of a pattern that is randomized in the width and lengthdirections with the initial basis shape shown in FIG. 63, once anappropriately compressed starting pattern is identified, the position ofat least some of the non-interlockable optical elements is shifted by arandom amount in each direction in which randomization is desired. Therandom amounts can either be chosen randomly from a predetermined set ofacceptable displacements or can be completely random. In either case anupper limit to the amount of random displacement, in a given direction,consistent with the amount of lattice compression, may be set to avoidundesirable patterning effects as well as the introduction of additionalnon-patterned area. FIGS. 65 and 66 show one example of a nonrandomizedpattern 105 and a randomized pattern 106 of non-interlockable wedgeshaped elements 5, respectively, that resulted from this process. Ifadditional non-patterned area is not a concern or is desirable for agiven application, then the compression of the lattice spacing need notbe done.

In addition to a single basis element that can be patterned in a twodimensional lattice with substantially complete surface coverage, morethan one basis element may also be used to create more complicatedlattices. Further, complex lattice structures with less thansubstantially complete surface coverage may also be used.

Moreover, a radial pattern of optical elements 5 may be provided on orin a surface 96 of an optically transparent substrate 8 of a lightredirecting film 2 with the optical elements overlapping andintersecting each other as schematically shown in FIG. 67.

Ideally the surfaces 10, 12 of the optical elements 5 that come togetherform distinct, non-rounded ridges 97 as schematically shown for examplein FIGS. 68 and 69 in order to maximize the on axis gain of lightexiting the light redirecting films. However, depending on themanufacturing process used to make the light redirecting films, theridges 97 may have one or more non-distinct ridge sections 110 that maybe rounded as schematically shown at 112 in FIGS. 70 and 72 but thatmore likely have flattened, rounded, curved or otherwise misshaped ridgepeaks 113 as schematically shown in FIGS. 71 and 73 due to incompletereplication or forming of the optical element shapes. Some of thisrounding of the ridges 97 or flattening or rounding of the ridge peaksdue to incomplete replication or forming of the ridges of the opticalelements is permissible for use of the film as a brightness enhancingfilm. However, the ratio of the total sidewall surface area (i.e. thesum of the surface areas of the sides or sidewalls 10,12) over the sumof the total area of the sides or sidewalls of the optical elements andthe rounded ridge sections 112 or flattened, rounded, curved orotherwise misshaped ridge peaks 113 should be equal to or greater than90% as determined by the following formula:

$\begin{matrix}{\frac{\sum\limits_{i = 1}^{n}A_{i}}{{\sum\limits_{i = 1}^{n}A_{i}} + {\sum\limits_{j = 1}^{m}B_{j}}} \geq 0.9} & \left. a \right)\end{matrix}$

where:

-   -   A_(i)=The surface area of the i^(th) sidewalls 10, 12 and    -   B_(j)=The surface area of the j^(th) rounded ridge sections 112        or flattened, rounded, curved or otherwise misshaped ridge peaks        113.    -   n=The number of sidewalls 10,12    -   m=The number of rounded ridge sections 112 or flattened,        rounded, curved or otherwise misshaped ridge peaks 113.        Alternatively, the ratio of the total sidewall surface area that        would be present if the optical elements ridge peaks were fully        replicated minus the total sidewall surface area that is missing        because of the rounded ridge sections 112 or flattened, rounded,        curved or otherwise misshaped ridge peaks 113, over the total        sidewall surface area that would be present if the optical        elements ridge peaks were fully replicated should be equal to or        greater than 90% as determined by the following formula:

$\begin{matrix}{\frac{{\sum\limits_{i = 1}^{n}\alpha_{i}} - {\sum\limits_{j = 1}^{m}\beta_{j}}}{\sum\limits_{i = 1}^{n}\alpha_{i}} \geq 0.9} & \left. b \right)\end{matrix}$

-   -   where:        -   α_(i)=The surface area of the i^(th) sidewalls 10, 12 if the            ridge 97 was fully formed or replicated, and        -   β_(j)=The sidewall surface area that is missing because of            the j^(th) rounded ridge sections 112 or flattened, rounded,            curved or otherwise misshaped ridge peaks 113.        -   n=The number of sidewalls 10,12 if the ridge 97 was fully            formed or replicated.        -   m=The number of rounded ridge sections 112 or flattened,            rounded, curved or otherwise misshaped ridge peaks 113.

In particular, for the wedge shape optical elements 5 having aflattened, rounded, curved or otherwise misshaped ridge peak 113 asshown for example in FIG. 73, the application of formula b above givesthe following, using the geometrical definitions given in FIG. 73. Thetotal sidewall surface area that would be present if the opticalelements ridge peaks were fully replicated (i.e. the sum of the surfaceareas of the sidewalls 10,12 in FIG. 68) is given by

(2−ξ)·sin(a cos(ξ))+(1−2·ξ)·a cos(ξ)  c)

and the total sidewall surface area that is missing because of theflattened, rounded, curved or otherwise misshaped ridge peak 113 isgiven by

(2−β)·sin(a cos(β))+(1−2·β)·a cos(β)  d)

where:

$\xi = {1 - \frac{\gamma}{2 \cdot R \cdot {\cos (\theta)}}}$$\beta = {1 - \frac{D}{R \cdot {\cos (\theta)}}}$

-   -   R=Radius of curvature of the curved side 12,    -   D=Peak depth or height of the optical element 5,    -   θ=Interior angle of the flat side 10 to the surface 96 of the        substrate 8, and        -   γ=Width of the flattened, rounded, curved or otherwise            misshaped ridge peak 113 (e.g., missing peak width) when            viewed from above and normal to the substrate as seen in            FIG. 73.            Substituting equations c and d into equation b above then            gives the equation:

${1 - \frac{{\left( {2 - \xi} \right) \cdot {\sin \left( {{acos}(\xi)} \right)}} + {\left( {1 - {2 \cdot \xi}} \right) \cdot {{acos}(\xi)}}}{{\left( {2 - \beta} \right) \cdot {\sin \left( {{acos}(\beta)} \right)}} + {\left( {1 - {2 \cdot \beta}} \right) \cdot {{acos}(\beta)}}}} \geq 0.9$

which if satisfied means that the light redirecting film may be used asa brightness enhancing film. If the ridges peaks 113 are more flattened,rounded, curved or otherwise misshaped than this, the film may not besuitable for use as a brightness enhancing film for most applicationsbecause the optical element shapes may not have enough sidewall surfacearea to obtain sufficient on axis gain.

FIGS. 74-78 show other light redirecting film systems 115 in accordancewith the present invention which are generally similar to the lightredirecting film system 1 shown in FIGS. 1 and 2. However, instead ofthe backlight BL having a substantially constant thickness as shown inFIGS. 1 and 2, FIGS. 74-78 illustrate that the backlights BL may begenerally wedge shape with their light emitting surfaces 116 taperinginwardly along their length as the distance from the light source 26increases. Also backlights BL may be designed such that the light rays Rexit from the backlights at very shallow angles. Because of this,different patterns of individual optical elements 5 may be placed on orin the light entrance surface 117 as shown in FIGS. 74 and 75, and ifdesired, on or in both the light entrance surface 117 and the light exitsurface 117′ of the light redirecting film 2 as shown in FIG. 76, forturning the light rays R received from the backlights BL and causing thelight to be directed at the associated displays D (which may for examplebe liquid crystal displays), within an acceptable angle, such that thelight emitted by the backlights will pass through the displays with lowloss. Also, two light redirecting films 2 may be placed between thebacklight BL and associated display D in overlying relation to oneanother with different patterns of optical elements 5 on or in the lightentrance surface 117 of one of the films and on or in the light exitsurface 117′ of the other film as shown in FIG. 77 or on the lightentrance surface 117 of both films as shown in FIG. 78. The light source26 shown in FIGS. 74 and 76-78 is a cold cathode fluorescent lamp 118,whereas the light source 26 shown in FIG. 75 is a light emitting diode119.

FIGS. 79 and 80 show still other light redirecting film systems 120 and122 in accordance with the present invention which are also generallysimilar to the light redirecting film system 1 shown in FIGS. 1 and 2.However, the light redirecting films or substrates 120 and 122 shown inFIGS. 79 and 80 overlie LCD TV backlights or other backlights 125 whichmay be comprised of light source arrays 126, for redirecting and shapingthe distribution of light rays R from the backlights through the display(not shown). In FIG. 79 the light source 126 comprises an array of coldcathode fluorescent lamps 127 suitably mounted on a tray or similar typesupport 128, whereas in FIG. 80 the light source 126 comprises an arrayof light emitting diodes 129 suitably mounted on a tray or similar typesupport 130. Each light emitting diode may have multiple colored chipsfor producing color or white light.

From the foregoing, it will be apparent that the light redirecting filmsof the present invention redistribute more of the light emitted by abacklight or other light source toward a direction more normal to theplane of the films. Also, the light redirecting films and backlights ofthe present invention may be tailored or tuned to each other to providea system in which the individual optical elements of the lightredirecting films work in conjunction with the optical deformities ofthe backlights to produce an optimized output light ray angledistribution from the system.

Although the invention has been shown and described with respect tocertain embodiments, it is obvious that equivalent alterations andmodifications will occur to others skilled in the art upon the readingand understanding of the specification. In particular, with regard tothe various functions performed by the above described components, theterms (including any reference to a “means”) used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed component which performs thefunction in the herein illustrated exemplary embodiments of theinvention. In addition, while a particular feature of the invention mayhave been disclosed with respect to only one embodiment, such featuremay be combined with one or more other features of other embodiments asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A light redirecting film comprising: a thinoptically transparent substrate having a light entrance surface and alight exit surface opposite the light entrance surface; and a pattern ofindividual optical elements formed as projections on the light exitsurface, the individual optical elements having a width and lengthsubstantially smaller than a width and length of the substrate, at leastsome of the projections comprising a dome-shaped surface on the lightexit surface.
 2. The light redirecting film of claim 1, wherein theindividual optical elements are randomized on the light exit surface. 3.The light redirecting film of claim 2, wherein the individual opticalelements randomly differ in density, size, height, position, slope ororientation on the light exit surface.
 4. The light redirecting film ofclaim 2, wherein the individual optical elements randomly overlap,intersect or interlock each other.
 5. The light redirecting film ofclaim 1, wherein the individual optical elements substantially cover aportion of the light exit surface.
 6. A light redirecting filmcomprising: a thin optically transparent substrate having a lightentrance surface and a light exit surface opposite the light entrancesurface; and a pattern of individual optical elements formed asprojections on a major surface of the substrate, the individual opticalelements having a width and length many times smaller than a width andlength of the substrate, at least some of the projections comprising arounded or curved top surface.
 7. The light redirecting film of claim 6,wherein the individual optical elements are randomized on the majorsurface.
 8. The light redirecting film of claim 7, wherein theindividual optical elements randomly differ in density, size, height,position, slope or orientation on the major surface.
 9. The lightredirecting film of claim 7, wherein the individual optical elementsrandomly overlap, intersect or interlock each other on the majorsurface.
 10. The light redirecting film of claim 6, wherein theindividual optical elements substantially cover a portion of the majorsurface.
 11. The light redirecting film of claim 6, wherein the majorsurface comprises the light exit surface.
 12. The light redirecting filmof claim 6, wherein the major surface comprises the light entrancesurface.
 13. The light redirecting film of claim 6, wherein at leastsome of the projections additionally comprise a side surface curvedalong a length thereof.
 14. The light redirecting film of claim 13,wherein the side surface of at least some of the projections intersectsthe major surface of the substrate.
 15. The light redirecting film ofclaim 14, wherein the intersection of the side surface of at least someof the projections with the major surface of the substrate forms atleast a portion of a curved or circular perimeter.
 16. The lightredirecting film of claim 14, wherein the major surface comprises thelight exit surface.